I am not a lawyer - However my own take on the AGPL is that if there's an external tool, an entirely separate process that is open source and does things, then as long as that source code is published and public a user is OK to use AGPL things.

As an example, let's say that I have a game. That game happens to want to have a way of rendering some HTML content for printing / making a PDF. It's OK to ship an open source thing with your game, like a hypothetical FrozenFluff web-browser licensed in AGPL. There are two distinct entities there: a FF binary that gets called with a file to render (which is AGPL and an AGPL processed result that is under the copyright of whomever's material was rendered) and another distinct binary the GameX that happened to call an external process.

The line to cross there is that the AGPL stuff can't be linked against your own program. I'm even more unsure how a module might or might not be licensed. I think since that's an addin then the code for the module (including headers) would have to be AGPL compatible and released, but that the rest could probably be closed.

This line is less clear when it comes to websites however. I think the best equivalent would be to make a wrapper interface that is AGPL licensed, published, and links to/calls the AGPL software. It should have a distinct URL. That URL might only be on the localhost (for security) and would hand back whatever results exist. The proprietary interface could talk to that URL and get results.